TLDR;
This video provides a comprehensive overview of the AQA GCSE Biology Paper 1, covering key topics such as cells, organization, infection and response, and bioenergetics. It explains cell structures, microscopy, and cell division, and also covers specialization, cloning, and transport mechanisms within cells. The video further discusses the organization of cells into tissues, organs, and systems, focusing on the digestive, respiratory, and circulatory systems, as well as the role of enzymes. Additionally, it addresses communicable and non-communicable diseases, plant structures, and the processes of photosynthesis and respiration.
- Cell structure and function, including microscopy and cell division (mitosis).
- Organization of cells into tissues, organs, and systems, with a focus on the human body.
- Communicable and non-communicable diseases, including causes, prevention, and treatment.
- Plant structure and function, including photosynthesis and respiration.
- Bioenergetics, covering photosynthesis, respiration, and metabolism.
Intro [0:00]
The video aims to quickly cover all essential topics for the AQA GCSE Biology Paper 1, suitable for both higher and foundation tiers, as well as combined trilogy and separate biology courses. The content includes cells, organization, infection and response, and bioenergetics. The presenter advises viewers to pause the video as needed to fully understand the information presented.
CELLS: Microscopy [0:27]
All life consists of cells, which can be observed using microscopes. Light microscopes allow visualization of cells and their nuclei, while electron microscopes provide higher resolution, revealing subcellular structures. Electron microscopes have better resolving power and higher resolution. Magnification is calculated as image size divided by object size, which can be rearranged to determine actual cell size.
Cell biology [1:04]
Cells are divided into two main groups: eukaryotic and prokaryotic. Eukaryotic cells, such as plant and animal cells, contain a nucleus where DNA is stored. Prokaryotic cells lack a nucleus. Both cell types contain organelles or subcellular structures. The cell membrane encloses the cell and is semi-permeable, allowing certain substances to pass through. Plant cells and bacteria have a cell wall made of cellulose, providing structural support. The cytoplasm is the liquid within the cell where chemical reactions occur. Mitochondria are the sites of respiration, producing energy for the cell. Ribosomes synthesize proteins. Plant cells also have chloroplasts containing chlorophyll for photosynthesis and a permanent vacuole for storing sap.
Microbiology practical (TRIPLE) [1:54]
Bacteria multiply through binary fission. Aseptic techniques are used to culture bacteria on agar in a petri dish, preventing contamination. This involves lifting the lid near a flame to eliminate airborne microbes and using sterilized equipment. A bacterial culture is placed in the middle or spread around the dish, and antibiotic spots can be added. The dish is taped, ensuring air can enter for aerobic respiration, and incubated at 25 degrees Celsius. After growth, the culture size or the area where antibiotics inhibited growth is measured and compared. The area of the circles is calculated using πr² or πd²/4.
Mitosis [2:47]
Eukaryotic cell nuclei contain DNA stored in chromosomes. Human cells have 23 pairs of chromosomes, making them diploid, except for gametes, which have 23 single chromosomes and are haploid. New cells are made for growth and repair through mitosis. During mitosis, genetic material is duplicated, the nucleus breaks down, and chromosome pairs are separated to opposite sides of the cell. New nuclei form around the copied chromosomes, resulting in two identical cells.
Specialisation & cloning [3:29]
Cells specialize based on their function, such as nerve, muscle, root hair, xylem, and phloem cells. Stem cells are unspecialized cells found in human and animal embryos and the meristem of plants. Bone marrow also produces stem cells that can only specialize into blood cells. Stem cells can be used to treat conditions like diabetes and paralysis. Cloning can produce stem cells that won't be rejected by a patient's body. Cloning plants can prevent extinction or produce crops with specific traits.
Diffusion, osmosis & active transport [4:14]
Diffusion is the movement of molecules from an area of high concentration to an area of low concentration, moving down the concentration gradient without energy input, making it a passive process. This occurs across a semi-permeable membrane if the molecules are small enough to pass through. Osmosis is specifically the diffusion of water across a semi-permeable membrane. If there's a higher concentration of glucose outside a cell, water will move out of the cell to balance the concentration, decreasing the cell's mass. The rate of diffusion and osmosis increases with higher concentration differences, higher temperatures, and larger surface areas, which is why villi in the small intestine, alveoli in the lungs, and root hair cells are lumpy.
ORGANISATION: Cells, tissues, organs [6:09]
Similar cells connected form a tissue, such as heart tissue. Tissues form organs, like the heart, and organs work together in an organ system, such as the circulatory system.
Digestive system [6:23]
The digestive system breaks down food into nutrients. Acid in the stomach begins the process, while bile and enzymes in the small intestine further break down the food. Bile, produced in the liver and stored in the gallbladder, neutralizes stomach acid and emulsifies fats, increasing their surface area for enzyme action.
Enzymes [6:47]
Enzymes are biological catalysts that break down large molecules into smaller ones, which are then absorbed into the bloodstream via the villi in the small intestine. Amylase, for example, breaks down starch into glucose and is found in the small intestine and saliva. Enzymes are specific, meaning they only break down certain molecules; carbohydrases break down carbohydrates, proteases break down proteins into amino acids, and lipases break down lipids into glycerol and fatty acids. Enzymes operate on a lock and key principle, where the substrate binds to the enzyme's active site to form a complex, but only if the substrate's shape matches the active site.
Food tests [8:50]
Food tests identify nutrients in food. Iodine turns from orange to black in the presence of starch. Benedict's solution turns from blue to orange in the presence of sugars. Biuret reagent turns from blue to purple with proteins. Cold ethanol turns cloudy with lipids (fats).
Respiratory system [9:10]
The respiratory system involves breathing and gas exchange. Breathing provides oxygen for respiration in cells. Air moves down the trachea, into the bronchi, then the bronchioles, and finally into the alveoli, where oxygen diffuses into the blood vessels. Alveoli are lumpy to increase surface area for fast gas exchange. Oxygen binds to hemoglobin in red blood cells and is transported to cells for respiration. Carbon dioxide from respiration dissolves into the blood plasma, diffuses into the lungs, and is exhaled.
The heart [9:49]
The heart is the center of the circulatory system, a double circulatory system where blood enters the heart twice per cycle. Deoxygenated blood from the body enters the right side of the heart through the vena cava into the right atrium. A valve prevents backflow. The heart muscle contracts, pushing blood through the pulmonary artery to the lungs for oxygenation. Oxygenated blood returns to the heart through the pulmonary vein into the left atrium, then to the left ventricle, and out to the body through the aorta. The left side of the heart has thicker walls because the left ventricle pumps blood to the entire body, while the right ventricle only pumps to the lungs. Electrical pulses from a group of cells cause the heart to beat; if these cells malfunction, an artificial pacemaker can be used.
Circulatory system [10:51]
Arteries carry blood away from the heart, while veins carry blood towards the heart. Arteries have thicker walls to withstand higher pressure and a thinner lumen (the hole in the middle). Veins have thinner walls due to lower blood pressure but have valves to prevent backflow. Arteries split into smaller capillaries with one-cell-thick walls for fast diffusion of molecules in and out of cells. The heart, being a muscle, receives oxygen and blood from the coronary artery. Blockage of this artery by fatty deposits can cause a heart attack, or coronary heart disease (CHD). Stents are inserted to keep blood vessels open, and statins reduce cholesterol to decrease fatty deposits. Faulty heart valves can be replaced with artificial ones. Blood also contains white blood cells for fighting infections and platelets for clotting wounds.
Non-communicable diseases [12:03]
Cardiovascular disease (CBD) is a non-communicable disease caused by internal factors. Other examples include autoimmune conditions and cancer. Communicable diseases are caused by pathogens like viruses, bacteria, or fungi. Obesity and high sugar intake can cause type 2 diabetes. Poor diet, smoking, and lack of exercise increase the risk of heart disease. Alcohol can cause liver diseases, and smoking can cause lung disease or cancer. Carcinogens, such as ionizing radiation, increase the risk of cancer. Cancer results from uncontrolled cell division, leading to tumors. Benign cancers don't spread and are easier to treat, while malignant cancers spread throughout the body and are more dangerous.
Plant structure [13:01]
Plants have organs such as leaves, where photosynthesis occurs, and water leaves the plant through transpiration. Roots absorb water and mineral ions. The meristem produces new cells. Xylem are continuous tubes that transport water unidirectionally via transpiration. Phloem transports sugars, food, and sap bidirectionally via translocation.
Leaf structure [13:58]
The rate of transpiration increases with higher temperature, lower humidity, and increased air movement, all of which cause faster water evaporation from the leaves. A cross-section of a leaf includes the waterproof waxy cuticle, which prevents water evaporation from the top. The upper epidermis consists of transparent cells that allow light to pass through to the palisade mesophyll layer, which is full of chloroplasts for photosynthesis. The spongy mesophyll layer has gaps for gas exchange, allowing carbon dioxide to diffuse in and oxygen and water to diffuse out. The vascular bundle includes the xylem and phloem. The lower epidermis has stomata (holes) for gas exchange, controlled by guard cells that regulate the size of the stomata.
INFECTION & RESPONSE: Communicable diseases & pathogens [15:04]
Communicable diseases are caused by pathogens: viruses, bacteria, fungi, or protists. Viruses are protein casings with genetic code that inject into cells, causing them to produce more viruses until the cell explodes. Measles is a virus spread by droplets that causes a rash. HIV is a sexually transmitted infection (STI) that compromises the immune system, also known as AIDS. Bacteria release toxins that damage body cells, such as salmonella from undercooked food or gonorrhea, another STI. Fungi, like athlete's foot, cause similar damage, while protists can cause diseases like malaria, which is spread by mosquitoes (the vector) and involves the protist burrowing into and destroying red blood cells. Plants are susceptible to fungal infections like rose black spot, which can be treated with fungicides, and tobacco mosaic virus, which inhibits chlorophyll production and stunts growth.
Defences & immune response [16:43]
The body protects itself from pathogens through several mechanisms. The skin acts as the first barrier, and mucus in the nose and trachea traps pathogens. Acid and enzymes in the digestive system destroy pathogens. If pathogens enter the bloodstream, white blood cells combat them. Lymphocytes produce antitoxins to neutralize poisons and antibodies that stick to antigens on pathogens, preventing them from infecting cells and clumping them together for phagocytes to ingest and destroy. Antigens have specific shapes, so only matching antibodies can neutralize them. If a pathogen is unknown, lymphocytes produce different antibodies until one fits, and the immune system stores a copy of this antibody and antigen for future use, providing immunity. Vaccines expose the immune system to dead or inert pathogens, allowing it to produce antibodies without causing infection.
Antibiotics & drug development [18:19]
Antibiotics kill bacteria but not viruses. Penicillin was the first antibiotic. Because there are good bacteria in the body, antibiotics are designed to be as specific as possible. However, bacteria can mutate and become resistant to antibiotics, making them less effective with overuse. Drugs used to be extracted from plants and other organisms, like aspirin from willow trees and penicillin from mold. Now, synthesizing drugs is a major industry. Drugs undergo trials to test effectiveness and check for side effects, starting with lab trials on cell tissue, then animal trials, and finally human trials. Human trials involve giving the drug to one group and a placebo (sugar pill) to a control group without informing them which they are receiving (blind trial). A double-blind trial is when even those analyzing the results are unaware of the group assignments to eliminate bias.
Monoclonal antibodies (TRIPLE) [19:19]
Monoclonal antibodies are made from clones of a cell that produces a specific antibody to combat a disease. This is achieved by combining lymphocytes from mice with tumor cells to create a hybrid cell, which is then cloned to produce many antibodies for patient treatment. These antibodies can also be used for medical diagnosis, pathogen detection, and identifying molecules in tissue by binding them to a dye that glows when grouped together. However, the side effects of monoclonal antibodies are proving to be worse than expected.
BIOENERGETICS: Photosynthesis [20:00]
Photosynthesis occurs in chlorophyll and chloroplasts in plant cells, providing food for the plant. The balanced chemical equation for photosynthesis shows that it is an endothermic reaction, requiring energy in the form of light. Glucose produced is used for respiration or converted into starch or fat for energy storage. Cellulose is used to produce cell walls, and amino acids are used for synthesizing proteins. The rate of photosynthesis increases with higher temperature (unless enzyme denaturing occurs), increased light intensity, or increased CO2 concentration, any of which can be a limiting factor.
Respiration & metabolism [21:32]
Every cell (except red blood cells) has mitochondria, where respiration takes place to provide energy for organisms for chemical reactions, movement, and warmth. Aerobic respiration requires oxygen. During exercise, breathing and heart rate increase to deliver more oxygen to cells for respiration. Anaerobic respiration occurs when there is a lack of oxygen, converting glucose into lactic acid and releasing less energy, causing muscle ache. This creates an oxygen debt, requiring more oxygen afterward to break down lactic acid in the liver, turning it back into glucose. Plant and yeast cells respire anaerobically, turning glucose into ethanol and carbon dioxide, which is why yeast is used in baking to make bread rise (fermentation). Metabolism is the sum of all reactions in a cell or organism, including respiration, conversion of glucose into starch, glycogen, and cellulose, building glucose into cellulose for cell walls, using glucose and nitrates to make amino acids for protein synthesis, building fatty acids and glycerol into lipids, and breaking down excess proteins into urea.